fix(hygiene): enforce source hygiene in CI #564

check_hygiene.py --check-simp flags a non-terminal bare simp at Complexity/Computability/Circuit/Boolean/CarryLookahead.lean:127, which #542 introduced. AGENTS.md requires simp only there. CI never runs check_hygiene.py: only local integration runs did, and they omitted --check-simp. So violations can reach main unnoticed.

Done when: the hit is fixed and CI runs check_hygiene.py --check-simp (about 13 s, no Lean build). Claimed by coordinator-claude-c4b0c164-20261023; branch fix/carry-lookahead-simp-only.